Understanding how water flows in the catchment

To effectively manage a catchment it is important to have a collective understanding of how the catchment works. This Map Journal gathers information from experts and other data sources to provide that understanding.

The information was gathered using the walking the landscape process, where experts systematically worked through a catchment in a facilitated workshop, to incorporate diverse knowledge on the landscape features and processes, both natural and human. It focussed on water flow and the key factors that affect water movement.

The Map Journal was prepared by the Queensland Wetlands Program in the Queensland Department of Environment and Science in collaboration with local partners.

How to View this Map Journal

Map Journal for the Mid Brisbane Catchment - water movement

This Map Journal describes the location, extent and values of the Mid Brisbane catchment. It demonstrates the key features which influence water flow, including geology, topography, rainfall and runoff, natural features and human modifications and land uses.

Knowing how water moves in the landscape is fundamental to sustainably manage the catchment and the services it provides.

Mid Brisbane catchment story

The Mid Brisbane catchment is located west of Brisbane between Wivenhoe Dam and Mount Crosby Weir, and falls within Ipswich City Council,Brisbane City Council and Somerset Regional Council boundaries and a very small part of Moreton Bay Regional Council.

The river stretches 61 kilometres and the catchment covers an area of about 522 square kilometres (click for animation).

It also recieves water from the much larger Lockyer catchment, and via Wivenhoe Dam, the Upper Brisbane and Stanley catchments. The Brisbane River continues below the Mid Brisbane catchment where it is joined by the Bremer,Lower Brisbane and Oxley catchments before reaching Moreton Bay.

Values of the Catchment

The Mid Brisbane catchment contains many environmental, economic and social values. The catchment has a population of more than 8,000 people, including the townships of Fernvale, Lowood and Marburg.The area contains a number of protected areas, including D'Aguilar National Park. The area also contains important aquatic species including platypus and lungfish.

Values of the Catchment

The catchment has large areas of fertile soils that supportintensive agriculture,grazing and rural living(use legend). There are also ample areas for land and water based recreational activities such as camping, canoeing, fishing, bush walking, mountain biking and horse riding.

Values of the catchment

One of the most important services provided by this catchment is the supply of drinking water to more than 3 million people in South East Queensland.

Water from Wivenhoe Dam travels to the Mount Crosby treatment plant and the smaller Lowood water treatment plant through the open river channel.Under normal water flow conditions it takes about 14 days. This can expose the water to an array of potential environmental factors including sediments and salinity.In the 2013 floods, Brisbane came within six hours of running out of treated drinking water because of the impact of sediment on the Mount Crosby Water Treatment Plant.

Natural features - geology and topography

On the northern side the landscape contains steep slopes which are underlain by fractured, relatively impermeable rocks which allow surface water to runoff with minimal infiltration.Creeks fill rapidly and have fast flows.

The southern side has more undulating landscapes that are underlain by sandstones, which have generally low permeability. Due to the undulating landscape, water flow rates are generally slower than those on the northern side.Some of thesesandstones contain naturally saline groundwater.Spring Creek is underlain by moreporous sandstone.

The remaining area is made up of permeable silts, sands and gravels and other materials deposited by rivers, called alluvium, and some areas ofbasalt.

Natural features – rainfall

The Mid Brisbane catchment experiences high to moderate rainfall, with the highest falls in the north-east of the catchment. The D'Aguilar Range creates a rain shadow effect, preventing higher falls from reaching the southern and western parts of the catchment.

Natural features – vegetation

Vegetation affects how water flows through the catchment, and this process isaffected by land use and management practices.

Historically, the hills of the Mid Brisbane River contained expanses of Eucalypt woodlands to open forestswith some wet Eucalypt open forests. Other areas of the catchment were made up ofopen forests of eucalypts on floodplains, and acacia dominated open forests, woodlands and shrublands, and some pockets of rainforest.

This vegetation slowed water, retaining it longer in the landscape and recharging groundwater aquifers,and reduced the erosion potential and the loss of soil from the catchment.

Modified features - vegetation and land use

Much of the catchment lying south of the Brisbane River has been cleared (click to see animation) for rural industries such asgrazing,intensive agricultureand animal production as well as residential and rural residential development, andsand and gravel extraction. Some areas of vegetationhave regrown since initial clearing.

These activities change the shape of the landscape and can modify water flow patterns.

*Please note the residential areas shown include rural residential as well as other residential area types.

*Please note sand and gravel extraction shown are within KRA (Key Resource Areas) only.KRAsare identified locations containing important extractive resources of state or regional significance worthy of protection for future use. Some KRAs include existing extractive operations.

Modified features - channels and infrastructure

Buildings and important infrastructure such as roads, railways and creek crossings create impermeable surfaces and barriers that redirect water through single points or culverts, leading to channeling of water. This increases the rate offlow and the potential for erosion.

Modifications to channels such asstraightening and diversions,can also increase flow rates.

Modified features - dams and weirs

Dams and weirs can also modify the natural water flow patterns, by holding water and controlling the timing and quantity of releases.

Wivenhoe Damis located immediately above the Mid Brisbane catchment. It stores water from the Upper Brisbane and Stanley River catchments.The dam was built for the dual purposes of providing a safe and reliable water supply for the region and for flood mitigation.

Water is released constantly from the dam into the Mid Brisbane River to supply the Mount Crosbyand Lowood water treatment plants, and for the irrigation of crops. Additional releases are also made when the dam exceeds its full supply level, to ensure capacity to mitigate flood events.

Modified features - dams and weirs

Lake Manchester Dam was built to supply some of Brisbanes water but due to natural variability in water quality, the lake is now mainly used for recreation. As releases seldom occur, there is limited natural flow from the lake, except when the lake overflows in flood events.

Splityard Creek Dam provides a hydroelectric power for peak power demand. Water is pumped back into the dam during times of low energy demand.

The catchment also has numerous rural water storages and weirs, which modify water flows.

Water flow

Water flows across the landscape into streams and eventually into the Mid Brisbane River.(click for animation)

The remaining water either sinks into the ground where it supports a variety of terrestrial and groundwater dependent ecosystems or is used for other purposes.

The upper reaches of the catchment have relatively steep slopes which create the potential for increased runoff which may lead to flooding in areas where the floodplain has restricted channels and gullies.

The restricted channels and gullies eventually flatten out to form waterways that meander across the floodplain.They pass through alluvial areas which store and release water, prolonging the time streams flow.

The subcatchments

A catchment is an area with a natural boundary (for example ridges, hills or mountains) where all surface water drains to a common channel to form rivers or creeks.*

Larger catchments are made up of smaller areas, sometimes called subcatchments.

The Mid Brisbane catchment consists of large and small subcatchments.

The characteristics of each subcatchment are different, and therefore water will flow differently in each one.

https://www.goldcoast.qld.gov.au/Council-region/About-our-city/Environment-sustainability/Protecting-our-environment/Managing-our-waterways/About-water-catchments

Splityard Creek and England Creek

The Splityard Creek and England Creek subcatchments are on the northern side of the Mid Brisbane catchment. The upper slopes are steep,with narrow channels. The terrain becomes undulating and eventually flattens out at the confluence with the Brisbane River.

The upper parts of the subcatchments contain rocks with relatively low permeability, where the water runs fast in times of flow. The area is often dry, except for dam seepage from Splityard Creek Dam. Due to the fast flows in the catchments, there is little to no alluvium.

The lower areas contain agricultural and extractive industries.

Branch Creek and Cabbage Tree Creek

The Branch and Cabbage Tree Creek subcatchments upper slopes are steep, with narrow channels. They are underlain by rocks with relatively low permeability. Much like England and Splityard Creeks, this results in fast flows with little to no infiltration, and little alluvium.

The upper sections contain mostly well vegetated conservation areas, and both creeks flow into Lake Manchester Dam.

Water released from Lake Manchester flows through a pipeline into the lower reaches of Cabbage Tree Creek.There islimited natural flow below the lake in Cabbage Tree creek, except when the lake overflows in flood events.

Mid Brisbane - main channel

The landscape around themain channel of the Brisbane River, near Lowood, is flat. Tunnel erosion and bank slips can occur in this area.Much of the area is used for agricultural and grazing industries.

Around Banks and Oaky Creeks, the upper slopes are steep, with narrow channels. These areas have high runoff due to the relatively low permeability of the underlying geology. There is little alluvium,and in the flatter areas of these creeks there is some erosion.

Further down the main channel, the landscape around Shelley Lagoon is undulating. The Lagoon itself is a perched wetland. Water is slow moving with low energy.

Spring Creek

Spring Creek has changed its course over time, and currently flows into the Mid Brisbane River just below Wivenhoe Dam. When high flow events occur in Lockyer Creek, water will flow across the floodplain, and into this sub-catchment. In addition, when there is significant discharge from Wivenhoe dam, water will flow up Spring creek.

Black Snake Creek

The Black Snake Creek sub-catchment has naturally saline groundwater due to the presence of the saline sandstones and comparatively low rainfall. Extensive clearing has increased salinity levels*.

The removal of vegetation increases surface water runoff. In drier times salt accumulates due to low water flow and high evaporation rates, exacerbating salinity and impacts on infrastructure.

Water quality in this sub-catchment is also affected by increased sediment loss through vegetation clearing as well as increased contaminants from septic tanks.

In high flow events the salt, contaminants and sediments can be flushed out of the sub catchment and into the Brisbane River.

**This dataset identifies areas of salinity described as part of the South East Queensland salinity project. Definition of categories:Slight <2.0 dS/m;Moderate 2.0 – 4.0 dS/m;Severe >8.0 dS/m

Sandy Creek

Sandy Creekis very similar to Black Snake Creek as the groundwater is naturally saline and the area receives lower rainfall. However this sub-catchment does not have the same salinity, contaminantor sediment loss issues.

This may be attributed to the sub catchment not being as modified. It has more vegetation, less reliance on groundwater for intensive agriculture, fewer septic tanks and less channel modification.

Borallon/Mount Crosby

At the lower end of the catchment is Borallon/Mount Crosby sub-catchment. The area containsrural residential areas, grazing, andnatural and protected areas.

Due to the many types ofimpermeable and low porosity rocks in the sub catchment, surface water runs offleading to fast creek flows.

Conclusion

The Mid Brisbane catchment shows how natural and modified features within the landscape impact on how water flows. These issues need to be managed to ensure that the residents of South East Queensland receive a safe and secure drinking water supply, and that impacts on the multitude of values within the catchment and downstream in the Brisbane River and Moreton Bay, are minimised.

Knowing how the catchment functions is also important for future planning, including climate resilience. With this knowledge, we can make better decisions about how we manage this vital area.

Acknowledgements

Developed by the Queensland Wetlands Program in the Department of Environment and Science in partnership with:

Ipswich City Council

Somerset Regional Council

Brisbane City Council

Council of Mayors South East Queensland

SEQ Catchments

Seqwater

Queensland Wetlands Program (2016)Walking the Landscape-Mid Brisbane catchment summary. Department of Environment and Science, Brisbane.

Photos provided by: the Department of Environment and Science, Department of National Parks, Sport and Racing, SEQ Catchments, Ipswich City Council

The Queensland Wetlands Program supports projects and activities that result in long-term benefits to the sustainable management, wise use and protection of wetlands in Queensland. The tools developed by the Program help wetlands landholders, managers and decision makers in government and industry.

Contact wetlands♲des.qld.gov.au or visit wetlandinfo.des.qld.gov.au

Data sources, links and information

Software Used

ArcGIS for Desktop|ArcGIS Online|Story Map Journal

Some of the information used to put together this Map Journal can be viewed on the QLD Globe.

The Queensland Globe is an interactive online tool that can be opened inside the Google Earth™application. Queensland Globe allows you to view and explore Queensland spatial data and imagery. You can also download a cadastral SmartMap or purchase and download a current titles search.

More information about the layers used can be found here:

Source Data Table

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Last updated: 25 August 2021